1. Field of the Invention
The present invention relates to an evaluation method for a silicon on insulator (SOI) substrate. In particular, it relates to a method for evaluating crystallographic properties of an SOI layer (semiconductor layer) on the base substrate of the bonded SOI substrate, and an evaluation processor for implementing this method.
2. Description of the Related Art
In an SOI substrate used in semiconductor device manufacturing, an SOI layer served as a semiconductor layer, such as a silicon (Si) layer, is provided on an insulating substrate such as a sapphire substrate, or on an insulating film on a semiconductor substrate. A bonded SOI substrate is prepared by bonding the SOI layer above a base substrate, so that the SOI layer being in contact with an insulating film such as a silicon oxide (SiO2) film formed on the base substrate. In the bonded SOI substrate, the SOI layer is used as an active region of a semiconductor device. Even if some crystal defects are introduced in the base substrate, the semiconductor device fabricated in the SOI layer disposed above the base substrate may still perform many functions. However, if a significant amount or number of crystal defects are introduced in the SOI layer serving as the active region of the semiconductor device, the semiconductor device may not sufficiently perform required functions.
For example, slip dislocations may possibly be induced in the SOI substrate due to an annealing procedure conducted during manufacture of the bonded SOI substrate. In manufacturing processes of a semiconductor device using the bonded SOI substrate, when the slip dislocations occur in the SOI layer, serving as the active region of the semiconductor device, a slight amount of heavy metals contained in the SOI substrate may be diffused into the SOI layer and trapped in the slip dislocations, due to thermal processing included in the manufacturing processes. The slip dislocations which trap the heavy metals in the active region of the semiconductor device may cause performance and operation problems of the semiconductor device, such as causing an excessive leakage current. On the other hand, as mentioned above, the slip dislocations induced in the base substrate may not produce a substantial affect on the operation of the semiconductor device. Accordingly, evaluation of the crystallographic quality of the SOI layer is an indispensable process for effectively manufacturing the semiconductor device. In addition, determination of whether crystal defects such as the slip dislocations have been created in the base substrate or the SOI layer of the SOI substrate is extremely important for manufacturing the semiconductor device.
X-ray topography is known as a method for evaluating crystal defects in a single crystal substrate, for example a Si substrate. Observation of the X-ray topography may allow evaluation of the crystal defects across the entire area of a large diameter semiconductor substrate. Accordingly, in comparison with evaluation methods using selective etching or transmission electron microscopy (TEM), non-destructive observation of crystal defects may be easily performed over a wider evaluation range.
In the bonded SOI substrate, crystal orientation between the SOI layer and the base substrate usually do not match. Accordingly, when observing the bonded SOI substrate by X-ray topography, the crystal defects in the base substrate may be evaluated, but those in the SOI layer cannot be evaluated appropriately.